Rational Design of a Highly Selective Near‐Infrared Two‐Photon Fluorogenic Probe for Imaging Orthotopic Hepatocellular Carcinoma Chemotherapy

Anchoring Au nanoclusters into coordination polymers: A novel approach toward ATP detection and its application

Adenosine triphosphate (ATP) is the main source of energy required for all life activities and is used as a biomarker for diseases such as cancer. It is of great significance to design a novel fluorescent probe with favorable performance for monitoring the changes of ATP concentration. Herein, a fluorescence probe named ZnCPs@AuNCs for ATP sensing was designed and fabricated by integrating AuNCs into ZnCPs. The emission intensity of AuNCs was greatly enhanced upon the formation of the ZnCPs@AuNCs nanocomposites, which may be attributed to ZnCPs restricting the molecular motion of AuNCs. Upon the introduction of ATP, the fluorescence intensity at 564 nm of ZnCPs@AuNCs is quenched. According to this phenomenon, a sensitive and reliable ATP sensing platform was established. Moreover, ZnCPs@AuNCs were incorporated into a poly (vinyl alcohol) matrix for the fabrication of fluorescent film, which exhibited solid-state fluorescence. Inspired by the remarkable fluorescent properties of ZnCPs@AuNCs, the fluorescent hydrogel was prepared by mixing ZnCPs@AuNCs with κ-carrageenan, which demonstrated a response to ATP and favorable self-healing ability. This work presents a perspective of ZnCPs@AuNCs in multiple applications such as biosensing, fluorescent film, and hydrogel construction.

Near-infrared fluorescent indolizine-dicyanomethylene-4H-pyran hybrids for viscosity imaging in living cells

The development of near-infrared organic fluorescent dyes with tunable emission profiles is highly required in the field of biological sensing and imaging. In this paper, we designed and synthesized two organic fluorescent dyes, DCM-1 and DCM-2, through the hybridization of indolizine and dicyanomethylene-4H-pyran skeleton. These two compounds show near-infrared fluorescence with emission maximum approximately at 640 and 680 nm, respectively. Notably, both DCM-1 and DCM-2 have specific responses to viscosity without being interfered by biological relevant species. Cell experiments demonstrate that DCM-1 and DCM-2 can detect dynamic changes in viscosity within living cells, suggesting their potential applications in chemical biology research.

Carboxylesterase Activatable Molecular Probe for Personalized Treatment Guidance by Analyte-Induced Molecular Transformation

Accurate visualization of tumor microenvironment is of great significance for personalized medicine. Here, we develop a near-infrared (NIR) fluorescence/photoacoustic (FL/PA) dual-mode molecular probe (denoted as NIR-CE) for distinguishing tumors based on carboxylesterase (CE) level by an analyte-induced molecular transformation (AIMT) strategy. The recognition moiety for CE activity is the acetyl unit of NIR-CE, generating the pre-product, NIR-CE-OH, which undergoes spontaneous hydrogen atom exchange between the nitrogen atoms in the indole group and the phenol hydroxyl group, eventually transforming into NIR-CE-H. In cellular experiments and in vivo blind studies, the human hepatoma cells and tumors with high level of CE were successfully distinguished by both NIR FL and PA imaging. Our findings provide a new molecular imaging strategy for personalized treatment guidance.

Enzyme-Activatable Near-Infrared Hemicyanines as Modular Scaffolds for in vivo Photodynamic Therapy

Photodynamic therapy is an anti-cancer treatment that requires illumination of photosensitizers to induce local cell death. Current near-infrared organic photosensitizers are built from large and non-modular structures that cannot be tuned to improve safety and minimize off-target toxicity. This work describes a novel chemical platform to generate enzyme-activatable near-infrared photosensitizers. We optimized the Se-bridged hemicyanine scaffold to include caging groups and biocompatible moieties, and generated cathepsin-triggered photosensitizers for effective ablation of human glioblastoma cells. Furthermore, we demonstrated that enzyme-activatable Se-bridged hemicyanines are effective photosensitizers for the safe ablation of microtumors in vivo, creating new avenues in the chemical design of targeted anti-cancer photodynamic therapy agents.

Remote Control of Energy Transformation-Based Cancer Imaging and Therapy

Cancer treatment requires precise tumor-specific targeting at specific sites that allows for high-resolution diagnostic imaging and long-term patient-tailorable cancer therapy; while, minimizing side effects largely arising from non-targetability. This can be realized by harnessing exogenous remote stimuli, such as tissue-penetrative ultrasound, magnetic field, light, and radiation, that enable local activation for cancer imaging and therapy in deep tumors. A myriad of nanomedicines can be efficiently activated when the energy of such remote stimuli can be transformed into another type of energy. This review discusses the remote control of energy transformation for targetable, efficient, and long-term cancer imaging and therapy. Such ultrasonic, magnetic, photonic, radiative, and radioactive energy can be transformed into mechanical, thermal, chemical, and radiative energy to enable a variety of cancer imaging and treatment modalities. The current review article describes multimodal energy transformation where a serial cascade or multiple types of energy transformation occur. This review includes not only mechanical, chemical, hyperthermia, and radiation therapy but also emerging thermoelectric, pyroelectric, and piezoelectric therapies for cancer treatment. It also illustrates ultrasound, magnetic resonance, fluorescence, computed tomography, photoluminescence, and photoacoustic imaging-guided cancer therapies. It highlights afterglow imaging that can eliminate autofluorescence for sustained signal emission after the excitation.

Design, synthesis, and evaluation of a carboxylesterase detection probe with therapeutic effects

In this study, a lysosomal targeting fluorescent probe recognition on CEs was designed and synthesized. The obtained probe BF2-cur-Mor demonstrated excellent selectivity, sensitivity, pH-independence, and enzyme affinity towards CEs within 5 min. BF2-cur-Mor could enable recognition of intracellular CEs and elucidate that the CEs content of different cancer cells follows the rule of HepG2 > HCT-116 > A549 > HeLa, and the CEs expression level of hepatoma cancer cells far exceeds that of normal hepatic cells, being in good agreement with the previous reports. The ability of BF2-cur-Mor to monitor CEs in vivo was confirmed by zebrafish experiment. BF2-cur-Mor exhibits some pharmacological activity in that it can induce apoptosis in hepatocellular carcinoma cells but is weaker in normal hepatocyte cells, being expected to be a potential "diagnostic and therapeutic integration" tool for the clinical diagnosis of CEs-related diseases.

Visualization of cysteine in AD mouse with a high-quantum yield NIR fluorescent probe

Alzheimer's disease (AD) has gradually received enthusiastic attention with the aging process, and studying its biological relevance is expected. Excitingly, fluorescence probes were considered to be powerful tools for exploring biological correlations. Therefore, a highly selective near-infrared (NIR) fluorescent probe (DCM-Cl-Acr) for imaging cysteine (Cys) in AD was designed and synthesized. Through structural optimization, the probe exhibited high fluorescence quantum yield and low detection limit (20 nM) towards Cys. Meanwhile, based on the high selectivity and high sensitivity response exhibited by the probe to Cys, it was successfully applied to visualize endogenous and exogenous Cys in living cells and zebrafish, and showed good discrimination from homocysteine (Hcy) and glutathione (GSH). Further, the correlation between AD and Cys concentration was clarified by imaging studies in hippocampus tissue of AD mouse, and the abnormal accumulation of Cys in the hippocampus of AD brain was demonstrated.

Dual-reporter fluorescent probe for precise identification of liver cancer by sequentially responding to carboxylesterase and polarity

Early treatment significantly improves the survival rate of liver cancer patients, so the development of early diagnostic methods for liver cancer is urgent. Liver cancer can develop from viral hepatitis, alcoholic liver, and fatty liver, thus making the above diseases share common features such as elevated viscosity, reactive oxygen species, and reactive nitrogen species. Therefore, accurate differentiation between other liver diseases and liver cancer is both a paramount practical need and challenging. Numerous fluorescent probes have been reported for the diagnosis of liver cancer by detecting a single biomarker, but these probes lack specificity for liver cancer in complex biological systems. Obviously, using multiple liver cancer biomarkers as the basis for judgment can dramatically improve diagnostic accuracy. Herein, we report the first fluorescent probe, LD-TCE, that sequentially detects carboxylesterase (CE) and lipid droplet polarity in liver cancer cells with high sensitivity and selectivity, with linear detection of CE in the range of 0-6 U/mL and a 65-fold fluorescence enhancement in response to polarity. The probe first reacts with CE and releases weak fluorescence, which is then dramatically enhanced due to the decrease in lipid droplet polarity in liver cancer cells. This approach allows the probe to enable specific imaging of liver cancer with higher contrast and accuracy. The probe successfully achieved the screening of liver cancer cells and the precise identification of liver cancer in mice. More importantly, it is not disturbed by liver fibrosis, which is a common pathological feature of many liver diseases. We believe that the LD-TCE is expected to be a powerful tool for early diagnosis of liver cancer.

Construction of a novel aminofluorene-based ratiometric near-infrared fluorescence probe for detecting carboxylesterase activity in living cells

Herein, we constructed a novel aminofluorene-based fluorescence probe (FEN-CE) for the detection of carboxylesterase (CE) in living cells by a ratiometric near-infrared (NIR) fluorescence signal. FEN-CE with NIR emission (650 nm) could be hydrolyzed specifically by CE and transformed to FENH with the release of the self-immolative group, which exhibited a red-shifted emission peak of 680 nm. In addition, FEN-CE showed high selectivity for CE and was successfully used in the detection of CE activity in living cells through its ratiometric NIR fluorescence signals.

Shining a light on liver health: advancements in fluorescence-enhanced enzyme biosensors for early disease detection

Early detection of liver diseases holds paramount importance in optimizing treatment outcomes and prognosis, thereby significantly enhancing the likelihood of recovery while mitigating the risk of progression to liver cancer. Liver diseases encompass a spectrum of conditions, each potentially manifesting distinct enzymatic profiles. Monitoring these enzymes in situ facilitates timely intervention and therapeutic management. In recent years, the field of biosensor technology has witnessed remarkable advancement, owing to strides in biomedicine and computational sciences. Biosensors have garnered widespread utility across medical and biological domains, spanning the detection of disease biomarkers, drug release tracking, ion imaging, and fluorescence imaging within living organisms. These applications have markedly enhanced imaging resolution and have the potential to refine disease diagnosis accuracy for clinicians. A pivotal aspect in the successful application of this technology lies in the construction of fluorescence probes adept at swiftly and selectively identifying target enzymes by amalgamating liver disease enzymes with fluorescence probe technology. However, research in this niche area remains relatively scarce. Building upon this foundational understanding, the present review delineates the utilization of biosensors in the early diagnosis of liver disease. Serving as a theoretical framework, this review envisages the development of high-performance biosensors tailored for the early detection of liver cancer. Furthermore, it offers insights into the potential of biosensor technology to progress and broaden its practical applications, thus contributing to the advancement of diagnostic methodologies in liver disease management.

Combination of two-photon fluorescent probes for carboxylesterase and ONOO- to visualize the transformation of nonalcoholic fatty liver to nonalcoholic steatohepatitis in liver orthotopic imaging

As the most common cause of liver diseases, nonalcoholic fatty liver disease (NAFLD) can be classified into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). While NAFL is generally benign, the transition from NAFL to NASH is a cardinal feature of the non-benign liver disease that leads to cirrhosis and cancer, which indicates that tracking the transformation of NAFL to NASH timely is significant for precision management of liver diseases. Therefore, two fluorescent probes (CNFCl and DRNO) have been developed to visualize this pathological event. α-Fluorochloroacetamide and α-ketoamide was employed as the recognition site for carboxylesterase (CE) in CNFCl and peroxynitrite (ONOO-) in DRNO, respectively. CNFCl (λem = 445 nm) and DRNO (λem = 560 nm) showed high specificity and sensitivity towards CE and ONOO- respectively. By incubating with CE/ONOO- for 0.5 h respectively, both the emission intensity of CNFCl (linear range: 0-0.2 U/mL) and DRNO (linear range: 0-17.5 μM) displayed significant enhancement. As a result, the detection limit of CNFCl and DRNO for CE and ONOO- was calculated as 4.2 mU/L and 0.05 μM respectively. More importantly, the emission spectra of CNFCl and DRNO in the presence of CE and ONOO- respectively were cross-talk free under the two-photon excitation of 720 nm. This greatly facilitated the simultaneous detection of CE and ONOO- at distinctive channel, thus ensuring the high fidelity of the detection. These two probes were combined to image the fluctuation of CE and ONOO- during the conversion of NAFL to NASH in vitro and in vivo. It was found that while CE displayed a tendency to rise and then reduce during the transition from NAFL to NASH, ONOO- increased continuously, confirming that the combined imaging by CNFCl and DRNO might visualize the transformation of NAFL to NASH. The results provide robust visual tool to decipher the relationship between the stage of NAFLD and the level of CE/ONOO-. We anticipate this study may open new avenues to distinguish NASH from NAFL, which may further promote the study of intracellular biological activities of CE and the development of NAFLD diagnostic methods.

An ultra-sensitive fluorescent probe for recognition of aluminum ions and its application in environment, food, and living organisms

The concentration of aluminum ions (Al3+) is closely related to the ecological environment, food safety, and human health, with excessive accumulation of Al3+ causing irreversible damage to both the ecological balance and human health. Therefore, a fluorescent probe ABHS, based on aminobenzoylhydrazide Schiff-base, was designed and synthesized in one step with a high yield. ABHS can form a 1:1 coordination complex with Al3+ in a pure water system. It exhibits ultra-sensitive and accurate detection of Al3+ even at low concentration of Al3+, with the detection limit of 6.7 nM. Furthermore, ABHS demonstrated significant enhancement of specific fluorescence for Al3+, with rapid response speed, good stability, and robust resistance to interference. Importantly, ABHS has shown excellent detection and imaging capabilities even in complex real environmental samples, food samples, and living organisms.

Co-Reactive Ligand In Situ Engineered Gold Nanoclusters with Ultra-Bright Near-Infrared Electrochemiluminescence for Ultrasensitive and Label-Free Detection of Carboxylesterase Activity

Ultrasensitive and accurate monitoring of carboxylesterase (CE) activity is extremely crucial for the early diagnosis of hepatocellular carcinoma (HCC), which is still a considerable challenge. Herein, using a co-reactive ligand engineering strategy, ultra-bright near-infrared (λmax = 830 nm) and self-enhanced electrochemiluminescence (ECL) Au nanoclusters (NCs) were in situ prepared with 2-(diethylamino) ethanethiol (DEAET) as a co-reactive ligand. Remarkably, the co-reactive ligand not only acts as a stabilizer like traditional ligands but also plays a crucial role as a co-reactant to ensure a confinement effect to shorten the charge transfer distance and increase the local concentration, significantly improving the collision efficiency between the electrogenerated free radicals. Consequently, the DEAET Au NCs exhibited a record and stable anodal ECL without the addition of an exogenous co-reactant, dramatically superior to classical Au NCs and Ru(bpy)32+ with a certain amount of the co-reactant. As a proof of concept, a convenient and label-free CE biosensor was innovatively constructed using 1-naphthyl acetate as a selective substrate, achieving ultrasensitive detection for CE activity with a low limit of detection of 9.1 × 10-7 U/L. Therefore, this work not only paves a co-reactive ligand engineering strategy for in situ preparation of high-efficiency metal NCs but also provides an ultrasensitive and convenient platform for the early diagnosis of HCC.

Promoting In Vivo NIR-II Fluorescent Imaging for Lipid in Lipid Metabolism Diseases Diagnosis

Lipid metabolism diseases have become a tremendous risk worldwide, along with the development of productivity and particular attention to public health. It has been an urgent necessity to exploit reliable imaging strategies for lipids and thus to monitor fatty liver diseases. Herein, by converting the NIR-I signal to the NIR-II signal with IR1061 for the monitoring of lipid, the in vivo imaging of fatty liver disease was promoted on the contrast and visual effect. The main advantages of the imaging promotion in this work included a long emission wavelength, rapid response, and high signal-background-ratio (SBR) value. After promoting the NIR-I signal to NIR-II signal, IR1061 achieved higher SBR value and exhibited a dose-dependent fluorescence intensity at 1100 nm along with the increase of the EtOH proportion as well as steady and selective optical responses toward liposomes. IR1061 was further applied in the in vivo imaging of lipid in fatty liver diseases. In spite of the differences in body weight gain and TC level between healthy mice and fatty liver diseases two models, IR1061 achieved high-resolution imaging in the liver region to monitor the fatty liver disease status. This work might be informatic for the clinical diagnosis and therapeutical treatments of fatty liver diseases.

Activatable Near-Infrared Versatile Fluorescent and Chemiluminescent Dyes Based on the Dicyanomethylene-4H-pyran Scaffold: From Design to Imaging and Theranostics

Activatable fluorescent and chemiluminescent dyes with near-infrared emission have indispensable roles in the fields of bioimaging, molecular prodrugs, and phototheranostic agents. As one of the most popular fluorophore scaffolds, the dicyanomethylene-4H-pyran scaffold has been applied to fabricate a large number of versatile activatable optical dyes for analytes detection and diseases diagnosis and treatment by virtue of its high photostability, large Stokes shift, considerable two-photon absorption cross-section, and structural modifiability. This review discusses the molecular design strategies, recognition mechanisms, and both in vitro and in vivo bio-applications (especially for diagnosis and therapy of tumors) of activatable dicyanomethylene-4H-pyran dyes. The final section describes the current shortcomings and future development prospects of this topic.

A "turn-on" red cyclometalated iridium (III) complex for long-term tracking the diffusion of CORM-2 in cells and zebrafish

Transition metal carbonyl compound of CO releasing molecules (CORMs) are widely used to treat arthritis, tumor and immune. They play a physiological role by directly acting on target tissues to release CO for disease treatment without matrix metabolism after dissolution. It is important to track the level and diffusion process of CORMs in vivo to control CO dose and distribution, facilitating to understand the roles of CORMs in disease treatment. Herein, we designed two red ring Ir1/2 complexes with a large stokes shift. Both Ir1 and Ir2 complexes probes can sensitively and selectively respond to CORM-2. The probe Ir1 exhibits rapid reaction with CORM-2 in Phosphate Buffered Saline within 1 min, showing a detection limitation of 0.13 μM and manifesting a linear relationship with the CORM-2 concentration from 0 to 70 μM at λem = 618 nm. Due to low toxicity even after 12 h exposure and fluorescence stability, this probe has been successfully used for continuous tracking the diffusion process of CORM-2 in living cells for up to 60 min and visualizing CORM-2 distribution in zebrafish. Additionally, this probe showed a good capacity for deep penetration (126 μm), suggesting the potential in detecting CORM-2 in living tissues.

Golgi-targeting viscosity probe for the diagnosis of Alzheimer's disease

Early diagnosis and intervention of Alzheimer's disease (AD) are particularly important to delay the pathological progression. Although fluorescent probes have been widely employed for investigating and diagnosing AD, their biological applications are significantly restricted due to the low penetration ability of the blood-brain barrier (BBB) in vivo. In this study, we reported the first Golgi-targeted two-photon (TP) fluorescent probe, DCM-DH, for detecting viscosity in the Golgi apparatus. The probe was rationally designed to exhibit superior analytical performance including high sensitivity, specific Golgi-targeting, efficient BBB penetration ability, and deep tissue penetration (247 μm) in the brains of AD model mice. Using the probe, we demonstrated that the fluorescence intensity in the human liver cancer cell (HepG2 cells) was higher than that of human normal liver cell (LO2 cells), and the brain viscosity of AD model mice increased significantly. We anticipate that this competent tool could be easily extended to other AD biomarkers for fundamental research on this detrimental disease.

A near-infrared fluorescent probe for viscosity: Differentiating cancer cells from normal cells and dual-modal imaging in tumor mice

As a basic parameter of the intracellular microenvironment, viscosity is closely related to the development of cancer. Thus, it is necessary to utilize a sensitive tool to visualize the viscosity in tumor cells and mice, which is helpful for the diagnosis of cancer. Herein, a novel dual-modal probe (IX-V) that has a near-infrared fluorescence (NIRF) and photoacoustic (PA) response to viscosity is synthesized. In low viscosity media, the probe has no fluorescence. With the increase of viscosity, the fluorescence is produced in the near-infrared region due to the inhibition of the TICT process. At the same time, the probe shows different photoacoustic (PA) signals in different viscosity media. Most notably, the viscosity in tumor cells has been imaged successfully by the application of IX-V, and the probe can effectively distinguish cancer cells from normal cells co-cultured in one dish by the difference of fluorescence intensity. In addition, the probe has been used for dual-modal imaging (NIRF and PA) of viscosity in tumor mice, which provides a tool for exploring the relationship between viscosity and diseases. That is to say, IX-V can achieve complementary imaging effects and has great application prospects in the tumor diagnosis.

Diketopyrrolopyrrole-based fluorescent probe for visualizing over-expressed carboxylesterase in fever via ratiometric imaging

Fever is the result of inflammation and the innate self-defense response of organisms, can cause abnormal changes in the activity of many enzymes in organisms, including the important carboxylesterase (CE). Monitoring the activity changes of CE in vivo during a fever will help to understand heat-related pathological mechanisms. In this paper, we designed diketopyrrolopyrrole-based ratiometric fluorescent probes DPP-FBC-P and DPP-FBO-P containing alkyl chain and diethylene glycol monomethyl ether chain respective for detection of CE. Both probes could realized fast response to CE and displayed good selectivity and high sensitivity. Compared with DPP-FBO-P, DPP-FBC-P had better biocompatibility, larger signal to noise ratio (225-fold vs 125-fold) and lower detection limit (1.6 × 10-5 U/mL vs 4.2 × 10-5 U/mL). Moreover, the probe DPP-FBC-P had been successfully applied to image the endogenous CE in HepG2 cells and solid tumors, and also visualized the over expressed CE in fever cells. Most importantly, the changes of CE level in the liver of fever mice model induced by LPS were monitored with the assistance of DPP-FBC-Pvia dual channel ratio imaging for the first time. In addition, fluorescence color signal in solution was captured by smart phone, and the linear relationship between RGB ratio (G/R) and CE concentration was established. This work will provide a potential approach for investigating the physiological and pathological processes of heat related diseases.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Tracing Superoxide Anion in Serotonergic Neurons of Living Mouse Brains with Depression by Small-Molecule Fluorescence Probes

In brains, the serotonergic neurons are the unique resource of the neurotransmitter serotonin, which plays a pivotal role in the physiology of the brain. The dysfunction of serotonergic neurons caused by oxidative stress in the brain is closely related to the occurrence and development of various mental diseases, such as depression. As the biomarker of oxidative stress, the superoxide anion radical (O2•-) can cause oxidative damage to proteins, nucleic acids and lipids, disturbing the function of neurons and brains. A serotonin transporter (SERT) specifically expresses in serotonergic neurons, which is the biomarker of serotonergic neurons. Thus, we created two novel small molecular fluorescent probes (PA-CA and HT-CA) for imaging O2•- in serotonergic neurons of living brains of mice based on specific targeting groups of SERT. Both PA-CA and HT-CA exert excellent SERT-targetable and glorious selectivity for O2•-. Those two probes could monitor the boost of O2•- in living hsert-HEK293 cells that specifically express SERT under oxidative stress. With two-photon fluorescence imaging, we revealed for the first time that O2•- is significantly increased in serotonergic neurons in living brains of mice with depression. More importantly, proteomic analyses suggested that O2•- could oxidize cysteine and histidine in the active site of SERT, which is involved in the development of depression. This work provides new materials for living brain imaging and offers new strategy for unraveling the pathophysiology of depression.

Rationally Engineered hCES2A Near-Infrared Fluorogenic Substrate for Functional Imaging and High-Throughput Inhibitor Screening

Human carboxylesterase 2A (hCES2A) is an important endoplasmic reticulum (ER)-resident enzyme that is responsible for the hydrolytic metabolism or activation of numerous ester-bearing drugs and environmental toxins. The previously reported hCES2A fluorogenic substrates suffer from limited emission wavelength, low specificity, and poor localization accuracy, thereby greatly limiting the in situ functional imaging of hCES2A and drug discovery. Herein, a rational ligand design strategy was adopted to construct a highly specific near-infrared (NIR) substrate for hCES2A. Following scaffold screening and recognition group optimization, HTCF was identified as a desirable NIR fluorophore with excellent photophysical properties and high ER accumulation ability, while several HTCF esters held a high potential to be good hCES2A substrates. Further investigations revealed that TP-HTCF (the tert-pentyl ester of HTCF) was an ideal substrate with ultrahigh sensitivity, excellent specificity, and a substantial signal-to-noise ratio. Upon the addition of hCES2A, TP-HTCF could be rapidly hydrolyzed to release HTCF, a chemically stable product that emitted bright fluorescent signals at around 670 nm. A TP-HTCF-based biochemical assay was then established for the high-throughput screening of potent and cell-active hCES2A inhibitors from an in-house compound library. Furthermore, TP-HTCF displayed high imaging resolution for imaging hCES2A in living cells as well as mouse liver slices and tumor-xenograft mice. Collectively, this study demonstrates a rational strategy for developing highly specific fluorogenic substrates for an ER-resident target enzyme, while TP-HTCF can act as a practical tool for sensing hCES2A in living systems.

Engineering a near-infrared LAP fluorescent probe with high sensitivity and selectivity for surgical resection of liver cancer

Hepatocellular carcinoma (HCC) is a type of cancer associated with a high rate of mortality and morbidity. In order to achieve precise HCC theranostics, it is important to develop excellent fluorescent probes. However, the existing probes are not sensitive or specific enough to accurately identify HCC margins and contours. For diagnosing HCC and identifying tumors during surgery, it is urgent to engineer highly sensitive and selective fluorescent probes. Liver tumor progression is closely associated with leucine aminopeptidase (LAP) overexpression, a biomarker of liver cancer. Herein, we have rationally designed a NIR fluorescent probe, NLAP, which is specially activated by LAP. The probe exhibited high sensitivity (detection limit = 6.8 mU L-1) and superior affinity (Km = 2.98 μM) for LAP. With this probe, we distinguished cancer cells overexpressing LAP from normal cells and applied it intraoperatively to guide liver tumor excisions. Furthermore, NLAP was employed to successfully detect the LAP of intestinal and splenic metastatic tumors in orthotopic liver tumor mice by "in situ spraying" and good performances were demonstrated.

Serum-Based Detection of Liver Pathology Using a Fluorogenic Alkaline Phosphatase Probe

Development of "ultrahigh contrast" fluorogenic probes for trapping alkaline phosphatase (ALP) activities in human serum is highly desirable for clinical auxiliary diagnosis for hepatobiliary diseases. However, the intrinsic dilemma of incomplete ionization of intramolecular charge transfer (ICT)-based ALP fluorophores and autofluorescence interference of serum result in low sensitivity and accuracy. Given that unique halogen effects could lead to a drastic decrease in the pKa value and a significant enhancement in the fluorescence quantum yield, herein we report an enzyme-activatable near-infrared probe based on a difluoro-substituted dicyanomethylene-4H-chromenep for achieving fluorescent quantification of human serum ALP. Rational design strategy is demonstrated by altering the substituted halogen groups to well regulate the pKa for meeting the physiological precondition. Owing to the complete ionization at pH 7.4 with tremendous fluorescence enhancement, the difluoro-substituted DCM-2F-HP manifests a linear relationship between the emission intensity and ALP concentration in both solution and serum samples. Along with measuring 77 human serum samples, the DCM-2F-HP based fluorescence method not only exhibits significant correlations with clinical colorimetry, but also distinguishes ALP patients from healthy volunteers, as well as assessing the progress of liver disease, thus providing a potential toolbox for quantitatively detecting ALP and warning the stage of hepatopathy.

A S-substituted Nile Blue-derived bifunctional near-infrared fluorescent probe for in vivo carboxylesterase imaging-guided photodynamic therapy of hepatocellular carcinoma

The development of theranostic probes that integrate both diagnostic and therapeutic functions still remains an intractable challenge in precise cancer treatment. Herein, a novel bifunctional near-infrared (NIR) fluorescent probe (CEP1) for carboxylesterase (CE) imaging and photodynamic therapy (PDT) of hepatocellular carcinoma (HCC) has been firstly developed and successfully applied in vitro and in vivo. The probe was constructed by introducing carbamate as both the recognition unit and the fluorescence quenching unit into the fluorophore S-substituted Nile Blue (ENBS) via a self-eliminating spacer with substituted chloride. It can be activated by CE and hydrolyzed into fluorescent ENBS, which recover fluorescence at about 700 nm, and can generate superoxide radical anions under NIR irradiation. Additionally, the probe could effectively distinguish tumor cells from normal cells by CE imaging of live cells. Furthermore, it could achieve CE imaging in vivo and significantly inhibits tumor growth by imaging-guided PDT. Therefore, this study offers a promising and attractive platform for activatable imaging-guided PDT of HCC.

Design of a near-infrared fluoro-photoacoustic probe for rapid imaging of carboxylesterase in liver injury

Carboxylesterase (CE) is crucial in metabolizing ester-containing biomolecules and is particularly significant in liver metabolic diseases. Herein, we present the first activatable NIRF/PA dual-mode imaging probe QHD-CE for detection of CE in vitro and in vivo. QHD-CE displays excellent sensitivity and selectivity for CE with a high reaction efficiency (∼90 min). By utilizing QHD-CE, the dynamic changes of CE in drug-induced liver injury and diabetic mice models were monitored.

Functional Nucleic Acid Probes Based on Two-Photon for Biosensing

Functional nucleic acid (FNA) probes have been widely used in environmental monitoring, food analysis, clinical diagnosis, and biological imaging because of their easy synthesis, functional modification, flexible design, and stable properties. However, most FNA probes are designed based on one-photon (OP) in the ultraviolet or visible regions, and the effectiveness of these OP-based FNA probes may be hindered by certain factors, such as their potential for photodamage and limited light tissue penetration. Two-photon (TP) is characterized by the nonlinear absorption of two relatively low-energy photons of near-infrared (NIR) light with the resulting emission of high-energy ultraviolet or visible light. TP-based FNA probes have excellent properties, including lower tissue self-absorption and autofluorescence, reduced photodamage and photobleaching, and higher spatial resolution, making them more advantageous than the conventional OP-based FNA probes in biomedical sensing. In this review, we summarize the recent advances of TP-excited and -activated FNA probes and detail their applications in biomolecular detection. In addition, we also share our views on the highlights and limitations of TP-based FNA probes. The ultimate goal is to provide design approaches for the development of high-performance TP-based FNA probes, thereby promoting their biological applications.

Orthogonally Engineered Albumin with Attenuated Macrophage Phagocytosis for the Targeted Visualization and Phototherapy of Liver Cancer

The five-year survival rate of hepatocellular carcinoma (HCC) remains unsatisfactory. This reflects, in part, the paucity of effective methods that allow the target-specific diagnosis and therapy of HCC. Here, we report a strategy based on engineered human serum albumin (HSA) that permits the HCC-targeted delivery of diagnostic and therapeutic agents. Covalent cysteine conjugation combined with the exploitation of host-guest chemistry was used to effect the orthogonal functionalization of HSA with two functionally independent peptides. One of these peptides targets glypican-3 (GPC-3), an HCC-specific biomarker, while the second reduces macrophage phagocytosis through immune-checkpoint stimulation. This orthogonally engineered HSA proved effective for the GPC-3-targeted delivery of near-infrared fluorescent and phototherapeutic agents, thus permitting target-specific optical visualization and photodynamic ablation of HCC in vivo. This study thus offers new insights into specificity-enhanced fluorescence-guided surgery and phototherapy of HCC through the orthogonal engineering of biocompatible proteins.

Multifunctional Theranostic Probe Based on the Pim-1 Kinase Inhibitor with the Function of Tracking pH Fluctuations during Treatment

Currently, kinase inhibitors have been applied in the diagnosis or treatment of cancer with their unique advantages. It is of great significance to develop some comprehensive theranostic reagents based on kinase inhibitors to improve the performance of reagents for biomedical applications. Besides, tracking changes in the intracellular environment (e.g., pH) during cancer development and drug delivery is also critical for cancer research and treatment. Therefore, it is an urgent desire to design some novel multifunctional reagents based on kinase inhibitor strategies that can trace changes in the microenvironment of cancer cells. In this paper, a multifunctional theranostic reagent based on Pim-1 kinase inhibitor 5-bromobenzofuran-2-carboxylic acid is proposed. The theranostic probe binds to tumor-specific Pim-1 kinase, releases strong fluorescence, and produces cytotoxicity, thus achieving cell screening and killing effects. Furthermore, the probe can specifically target lysosomes and sensitively respond to pH. It can be used to track the pH changes in the intracellular environment under conditions of autophagy and external stimulation, as a visual tool to monitor pH fluctuations during cancer treatment. In conclusion, this simple but multifunctional theranostic reagent proposed in this work is expected to provide a promising method for cancer diagnosis and therapy.

The rational utilization of organelle microenvironment for imaging of lysosomal SO2 with high fidelity

Nowadays, more and more studies have linked the abnormal expression of active molecules in organelles with the occurrence of diseases, so there is an urgent need to develop tools for detecting active molecules in specific organelles. However, the recognition receptors of most organelle-targeting probes currently developed always remain active, which easily causes them to react with the analyte in the cytoplasm, thus misjudging the role of the analyte in the physiological and pathological processes. Therefore, it is of great significance to develop a new strategy for the design of probes capable of high-fidelity imaging of the analyte in specific organelles. Herein, we propose a new strategy that the activation of recognition receptors that can be triggered by the microenvironment of targeting organelles. Based on this strategy, we develop a novel lysosome-targeting fluorescent probe (Lyso-SO₂) for imaging of sulfur dioxide (SO₂) with high-fidelity in lysosomes. The inert probe is activated by the acidic environment in the lysosome and then responds quickly (<2 s) and sensitively (LOD = 0.34 μM) to SO₂. This paradigm by taking full advantage of the features of the organelle microenvironment provides a promising methodology for developing organelle-targeting probes for high-fidelity imaging.

A dual-channel fluorescent nanoprobe for accurate cancer diagnosis by sequential detection of adenosine triphosphate and sulfur dioxide

Cancer is one of the major diseases that seriously endanger the health of all mankind. Accurate diagnosis of early cancer is the most promising way to reduce cancer harm and improve patient survival. However, many developed fluorescent probes for cancer imaging only have the function of identifying one marker, which cannot meet the needs of accurate diagnosis. Here, a fluorescent nanoprobe (CPH@ZIF-90) utilizing ZIF-90 to encapsulate SO₂-sensitive dye (CPH) is synthesized for the sequential detection of ATP and SO₂. The nanoprobe first interacts with ATP to release CPH, thus increasing the fluorescence at 685 nm and realizing the near-infrared (NIR) fluorescence detection of ATP. Then, SO₂ acts on the released CPH through nucleophilic addition, affecting the π-conjugated structure of CPH and resulting in enhanced fluorescence at 580 nm. CPH@ZIF-90 exhibits satisfactory sensitivity and selectivity for sequential detection of ATP and SO₂. Excitedly, CPH@ZIF-90 can sequentially image the endogenous ATP and SO₂ in cells, showing sensitive fluorescence changes in dual channels (red and green). Due to the NIR emission properties of CPH@ZIF-90 and its ability to enrich in tumor, it is applied to monitor ATP and SO₂ in mice and distinguish normal mice from tumor mice. The ability of CPH@ZIF-90 to sequentially detect two cancer-related biomarkers makes it provide meaningful assistance in accurate early diagnosis of cancer.

Cellular-scale proximity labeling for recording cell spatial organization in mouse tissues

Proximity labeling has emerged as a powerful strategy for interrogating cell-cell interactions. However, the nanometer-scale labeling radius impedes the use of current methods for indirect cell communications and makes recording cell spatial organization in tissue samples difficult. Here, we develop quinone methide-assisted identification of cell spatial organization (QMID), a chemical strategy with the labeling radius matching the cell dimension. The activating enzyme is installed on the surface of bait cells, which produces QM electrophiles that can diffuse across micrometers and label proximal prey cells independent of cell-cell contacts. In cell coculture, QMID reveals gene expression of macrophages that are regulated by spatial proximity to tumor cells. Furthermore, QMID enables labeling and isolation of proximal cells of CD4⁺ and CD8⁺ T cells in the mouse spleen, and subsequent single-cell RNA sequencing uncovers distinctive cell populations and gene expression patterns within the immune niches of specific T cell subtypes. QMID should facilitate dissecting cell spatial organization in various tissues.

Dual-Mode Ratiometric Electrochemical and Turn-On Fluorescent Detection of Butyrylcholinesterase Utilizing a Single Probe for the Diagnosis of Alzheimer's Disease

Biomarkers detection in blood with high accuracy is crucial for the diagnosis and treatment of many diseases. In this study, the proof-of-concept fabrication of a dual-mode sensor based on a single probe (Re-BChE) using a dual-signaling electrochemical ratiometric strategy and a "turn-on" fluorescent method is presented. The probe Re-BChE was synthesized in a single step and demonstrated dual mode response toward butyrylcholinesterase (BChE), a promising biomarker of Alzheimer's disease (AD). Due to the specific hydrolysis reaction, the probe Re-BChE demonstrated a turn-on current response for BChE at -0.28 V, followed by a turn-off current response at -0.18 V, while the fluorescence spectrum demonstrated a turn-on response with an emission wavelength of 600 nm. The developed ratiometric electrochemical sensor and fluorescence detection demonstrated high sensitivity with BChE concentrations with a low detection limit of 0.08 μg mL^-1 and 0.05 μg mL^-1, respectively. Importantly, the dual-mode sensor presents the following advantages: (1) dual-mode readout can correct the impact of systematic or background error, thereby achieving more accurate results; (2) the responses of dual-mode readout originate from two distinct mechanisms and relatively independent signal transduction, in which there is no interference between two signaling routes. Additionally, compared with the reported single-signal electrochemical assays for BChE, both redox potential signals were detected in the absence of biological interference within a negative potential window. Furthermore, it was discovered that the outcomes of direct dual-mode electrochemical and fluorescence quantifications of the level of BChE in serum were in agreement with those obtained from the use of commercially available assay kits for BChE sensing. This method has the potential to serve as a useful point-of-care tool for the early detection of AD.

Recent progress of TP/NIR fluorescent probes for metal ions

Metal ions are of significance in various pathological and physiological processes. As such, it is crucial to monitor their levels in organisms. Two-photon (TP) and near-infrared (NIR) fluorescence imaging has been utilized to monitor metal ions because of minimal background interference, deeper tissue depth penetration, lower tissue self-absorption, and reduced photodamage. In this review, we briefly summarize recent progress from 2020 to 2022 of TP/NIR organic fluorescent probes and inorganic sensors in the detection of metal ions. Additionally, we present an outlook for the development of TP/NIR probes for bio-imaging, diagnosis of diseases, imaging-guided therapy, and activatable phototherapy.

A Space-Dependent 'Enzyme-Substrate' Type Probe based on 'Carboxylesterase-Amide Group' for Ultrafast Fluorescent Imaging Orthotopic Hepatocellular Carcinoma

Fast and selective fluorescence imaging for a biomarker to related-disease diagnosis remains a significant challenge due to complex physical environment. Human carboxylesterase (CE) is expected to be a potential biomarker of hepatocellular carcinoma (HCC) to improve the accuracy of diagnosis. However, existing probes for CE has slow response rate and low selectivity. Herein, the amide group is selected as CE-responsive sites based on the "substrate-hydrolysis enzymatic reaction" approach. From a series of off-on probes with leave groups in the amide unit, probe J_Fast is screened with the optimal combination of rapid response rate and high selectivity toward CE. J_Fast requires only 150 s to reach the maximum fluorescence at 676 nm in the presence of CE and free from the interference of other esterase. Computational docking simulations indicate the shortest distance between the CE and active site of J_Fast . Cell and in vivo imaging present that the probe can turn on the liver cancer cells and tumor region precisely. Importantly, J_Fast is allowed to specifically image orthotopic liver tumor rather than metastatic tumor and distinguish human primary liver cancer tissue from adjacent ones. This study provides a new tool for CE detection and promotes advancements in accurate HCC diagnosis.

A Biocompatible Probe for the Detection of Neutrophil Elastase Free from the Interference of Structural Changes and Its Application to Ratiometric Photoacoustic Imaging In Vivo

Neutrophil elastase (NE) plays a key role in chronic inflammation and acute responses to infection and injury. Effective disease interventions thus call for precise identification of NE to aid the clinical treatment of such diseases. However, the detection process suffers from the interference of structural changes of NE. Herein, we introduce a molecular probe with high biocompatibility to overcome the interference, which was achieved by combining theoretical calculations and experimental studies, that permits highly specific and sensitive detection of NE in cells and in vivo. The upregulated NE accumulation was specifically measured in inflammation by ratiometric photoacoustic and near-infrared fluorescence imaging, providing a new method for developing more specific fluorogenic probes for other enzymes.

Rational design of a turn-on near-infrared fluorescence probe for the highly sensitive and selective monitoring of carboxylesterase 2 in living systems

In vivo selective fluorescence imaging of carboxylesterase 2 (CES2) remains a great challenge because existing fluorescence probes can potentially suffer from interference by other hydrolases. In addition, some fluorescent probes that have been separately reported for measuring CES2 activity in vitro are affected by autofluorescence and absorption of the biological matrix due to their limited emission wavelength or short Stokes shift. Herein, based on the substrate preference and catalytic performance of CES2, a novel and NIR fluorescent probe was developed, in which a hemi-cyanine dye ester derivative was used as the basic fluorescent group. In the presence of CES2, the probe was hydrolyzed to expose the fluorophore CZX-OH (λ_abs ∼ 675 nm, λ_em ∼ 850 nm), which led to a notable red-shift in the fluorescence (∼175 nm) spectrum. Confocal imaging of cells and live mice demonstrated that the fluorescent signal of this probe was related to the real activities of CES2 in cancer cells. All these results will powerfully promote the screening of CES2 regulators and the analysis of CES2-related physiological and pathological processes.

Monitoring cell viability in N-nitrosodiethylamine induced acute hepatitis and detection of hydrazine in solution and gas phase with Dual-function fluorescent probes

The highly toxic N-nitrosodiethylamine (NDEA) and hydrazine (N₂H₄) caused severe environmental contamination and serious health risks. Herein, we designed the two-photon ratiometric fluorescent probe (Nap-2), emission maximum shifted from 466 nm to 571 nm, to monitor cell viability of NDEA induced acute hepatitis via esterase activity detection. Furthermore, the probe Nap-2 evaluate the hydrazine (N₂H₄) content in the solution and gas phase. It is worth mentioning that we used NDEA induced acute hepatitis in the mice and evaluated the negative correlation of esterase activity in the tissue cells and serum with Nap-2. The probe Nap-2 exhibited that acute hepatitis induced by NDEA decreased cell viability. Furthermore, we made convenient test papers using Nap-2 to detect N₂H₄ in solution and gas phase. After adding N₂H₄, the fluorescence color changed from blue to yellow and was visible to the naked eye. This work provides a convenient tool and method for evaluating the toxicity of NDEA induced acute hepatitis and detecting N₂H₄ in the environment.

An enzyme activated fluorescent probe for LTA4H activity sensing and its application in cancer screening

Early diagnosis of cancer is an efficient strategy to prevent tumor progression and improve the survival rate of patients. However, to discovery of reliable tumor-specific biomarkers remains a great challenge. Leukotriene A4 hydrolase (LTA₄H) is a bifunctional zinc metalloenzyme with epoxide hydrolase activity and aminopeptidase activity, which plays important roles in allergic and inflammatory reactions and showed strong relevance with carcinoma progression. We thus sought to investigate the possibility of application LTA₄H activity detection in cancer diagnosis. To achieve this, we herein develop an enzyme activated fluorescent probe for LTA₄H activity sensing by incorporating the specific recognition unit of LTA₄H with a red-emitting fluorophore. The acquired probe (named as ADMAB) showed high sensitivity and specificity toward LTA₄H in vitro. By further application of ADMAB in living cells, significantly elevated LTA₄H activity in cancer cell lines was observed when compared with normal cell lines and in vivo tracing A549 tumor in nude mice was also realized by ADMAB. Meanwhile, the wound-healing assay further revealed the importance of LTA₄H in tumor metastasis. Moreover, the LTA₄H activity in human serum sample was successfully detected by ADMAB and significantly elevated LTA₄H activity in patients diagnosed with cancer was firstly found, which demonstrated ADMAB to be a useful tool for cancer diagnosis and LTA₄H related biological study.

Portable ratiometric fluorescence analytical device for copper ions based on smartphone in environment and living organisms

The concentration of copper ions (Cu²⁺) in the environment is closely related to water quality, food, and biological health. As an indispensable metal element for the human body, its content is closely related to many diseases. However, the current detection methods for Cu²⁺ have some limitations, such as complicated operations and unfavorable on-site analysis. Therefore, this work constructs a novel ratiometric fluorescent probe (QLP), which has the advantages of rapid response, good anti-interference ability and high sensitivity. It has been successfully used for the detection of Cu²⁺ in water samples, soil, and food. In addition, low cytotoxicity and strong tissue penetration make it suitable for the detection of Cu²⁺ in living cells and zebrafish, offering a chemical tool for exploring the physiological and pathological processes related to Cu²⁺. It is important to use probe QLP and portable UV lamp to create an easy-to-operate Cu²⁺ detection platform, which can quickly detect Cu²⁺ on-site by combining with a smartphone. This work not only provides a detection tool for on-site analysis of Cu²⁺, but also provides a reference strategy for the development of on-site detection methods for other environmental pollutants.

De Novo Design of Activatable Photoacoustic/Fluorescent Probes for Imaging Acute Lung Injury In Vivo

Effective monitoring of the physiological progression of acute lung injury (ALI) in real time is crucial for early theranostics to reduce its high mortality. In particular, activatable fluorescence and photoacoustic molecule probes have attracted attention to assess ALI by detecting related indicators. However, the existing fluorophores often encounter issues of low retention in the lungs and slow clearance from the body, which compromise the probe's actual capability for in situ imaging by intravenous injection in vivo. Herein, a novel near-infrared hemicyanines fluorophore (FJH) bearing a quaternary ammonium group was first developed by combining with the rational design and screening strategy. The properties of good hydrophilicity and blood circulation effectively enable FJH accumulation for lung imaging. Inspired by the high retention efficiency, the probe FJH-C that turns on fluorescence and photoacoustic signals in response to the ALI indicator (esterase) was subsequently synthesized. Notably, the probe FJH-C successfully achieved the selectivity and sensitivity toward esterase in vitro and in living cells. More importantly, FJH-C can be further used to assess lipopolysaccharides and silica-induced ALI through the desired fluo-photoacoustic signal. Therefore, this study not only shows the first activatable probe for real-time imaging of lung function but also highlights the fluorophore structure with high lung retention. It is believed that FJH and FJH-C can serve as an efficient platform to reveal the pathological progression of other lung diseases for early diagnosis and medical intervention.